The present invention relates to chromate conversion coatings to be applied to aluminum surfaces to provide a corrosion resistant coating thereon. The coating formed is also especially useful in forming an improved bond for organic finishes such as paints, lacquers, and the like, when desired.
Chromate conversion coatings are well known in the prior art. Numerous ions have been utilized in the preparation of these chromate coatings in addition to the chromium ion. The average composition which is utilized provides coatings which, in general, are highly colored in the nature of yellow, brown, or blue. When it is desired to apply paint to these surfaces, it is extremely disadvantageous to have the highly yellow color, particularly when a pastel paint is used since a greater quantity of paint must be used to overcome the underlying color.
It has now been found that a clear chromate conversion coating can be provided which will also provide the corrosion resistance necessary in protecting aluminum in situations where the surface is to be painted.